The present invention relates generally to reducing the noise in physiological signals. In particular the present invention relates to monitoring the medical condition of a woman in labor and to reducing the signal noise while processing abdominal surface electromyogram (EMG) signal data for the purpose of uterine contraction monitoring.
The present technology for monitoring uterine contraction uses a tocodynamometer, which measures the abdominal pressure exerted on a belt placed around the lower abdomen of a patient in labor. However, the tocodynamometer can be uncomfortable for some patients to wear. Additionally, abdominal pressure changes can be harder to detect on larger women. Enhanced uterine contraction monitoring through processing abdominal surface EMG signal data promises to provide obstetricians with an improved tool to diagnose whether a patient is at risk of preterm labor. Because premature birth is the leading cause (85%) of infant death, improved abdominal surface EMG technology holds the potential to advance prenatal care and management.
It has been well established that uterine contractions are caused by electrical potentials generated and propagated by muscle cells. These electrical activities occur in bursts and give rise to measurable electric fields called electromyographic (EMG) signals. The amplitude, frequency, and duration, of certain features of the EMG signals correspond to the frequency, duration, and effectiveness of the uterine contractions. The temporal and spectral characteristics of an EMG signal, recorded by external electrodes, make it possible to discriminate between efficient and inefficient contractions in terms of electrical command capability. It is also reported that the spectral density of the EMG signals shifts significantly at different stages during gestation, providing a means of separating non-laboring contractions from laboring contractions. It is possible to record uterine electrical activity as early as a gestational age of 19 weeks. Therefore, an abdominal EMG signal can be of value for pregnancy monitoring.
It is known that the EMG signal can be reliably recorded by placing electrodes on the internal uterine surface. However, such a procedure is both invasive and not accepted in clinical use. It has been proposed that the EMG signals should be acquired on the exterior surface of the abdomen, and this procedure has been shown to work in practice. EMG signals acquired in from the exterior surface of the abdomen can be used to detect and monitor contractions, due to the relationship between the onset of contraction and the spectral characteristics of the EMG signal. The main obstacles to such a use of EMG technology are, first, patient motion which causes noise and signal artifacts, second, interference from other physiological electrical events (such as Electrocardiogram (ECG)), and, third, imperfect electrode contacts.
There is a need for an effective means of reducing noise and more accurately processing the EMG signals received by the electrodes attached on the external abdominal wall, in order to extract from the EMG signal an indication of when the periods of contraction occur.
Briefly, in accordance with one embodiment of the present invention, a system is provided for reducing noise in electromyogram (EMG) signals acquired from the external abdominal surface to determine uterine contractions. The system comprises an EMG1 sensor configured to detect a first EMG signal and to generate a corresponding EMG1 input signal and an EMG2 sensor configured to detect a second EMG signal and to generate a corresponding EMG2 input signal. A signal processor is coupled to the EMG1 sensor and the EMG2 sensor. The signal processor processes the EMG1 input signal and the EMG2 input signal with a filter and sum technique to technique to generate an EMG1 reduced noise signal that represents a magnitude of at least one contraction event and periodicity of a set of multiple contraction events.
In accordance with another embodiment of the present invention, a method is provided for processing the first EMG signal and the second EMG signal from an abdominal surface to detect uterine contractions. The method comprises detecting the first EMG signal and generating the EMG1 input signal and detecting a second EMG signal and generating the EMG2 input signal. Processing the EMG1 input signal and the EMG2 input signal using the filter and sum technique to generate the EMG1 reduced noise signal.